What to do when your startup grows up?

I've been with my employer since the startup days about 4 years ago now. I'm not a founder, but I'm one of the earlier employees. The company is now profitable. The startup feel is gone. The quick-n-dirty, put something great together, fly-by-the-seat-of-your-pants, work late nights, brainstorm new ideas feel of the company is gone. Now there are measure-twice, cut once policies & procedures in place. Strict working schedules. No changes to production code without written approval from everyone above me. People get chewed-out now instead of congratulated. It sucks. I would leave if it weren't for the outstanding stock that the company is using as a carrot on a stick to keep me on the corporate treadmill. My question is: For those of you who live an breathe startups, what would you do? Would you stick with the company to age into the rest of your promised equity even though the work environment isn't what I joined when I signed on, or would you cut your losses and move to another startup with the hopes of greener pastures?